I first noticed this problem in the 195 driver, but it's still present in 256.25 and 256.29.

I have a Dell Precision M4400 with Quadro 770M. After going into standby and resuming, the driver no longer turns off the backlight when the display goes idle. Instead, it goes to full brightness, and the framebuffer is all white. The same occurs if you just close the laptop lid - instead of turning off the backlight, it turns it on at full brightness and you can see bright white light shining thru the gap between the lid and the laptop body.

On a separate note, whenever I use the Nvidia Settings applet and select GPU 0 Thermal Settings the applet immediately crashes.

The applet bug is just a minor annoyance, the backlight bug is quite aggravating because it's a drain on the battery.

Thanks for the clarification. When you said you first noticed the problem in the 195 driver, I thought that you meant that you hadn't noticed it in driver version before that.

When you say that `xset force dpms off` does the same thing once it starts happening, do you mean that turning DPMS off when the machine has not been on for a very long time works normally, but after it has been on for a while, it will fail?

A quick experiment that might point to whether this issue exists in the NVIDIA driver is to run your X server with the vesa driver, and try to induce the problem.

Right. On a fresh cold boot, "xset dpms force off" turns off the backlight. When the problem starts happening, this command has the same effect - backlight on full, screen all white. I wish I could identify one specific cause of it, but so far no idea.

I could try the vesa driver, but it might take a few days for any problem to surface. Won't really have conclusive evidence one way or the other.

I also was wondering if this could somehow be related to VDPAU accelerated video playback, because nothing else I do on this machine is particularly relevant to the GPU. But I do occasionally watch H264 videos with mplayer and vdpau. But I haven't been able to reproduce it from that yet either.